Theoretical models that deal with praxis divide the action plan into two major components: an executive-conceptual system and a production system. We define ideational apraxia as a conceptual disorder where a brain damaged patient has lost conceptual knowledge related to tool use and not necessarily performance knowledge. We propose that this conceptual disorder may occur at 3 different levels: 1. a brain damaged patient may not be able to associate a tool or instrument with the object or objects that usually receive the action of that tool. For example, a patient may not be able to associate a hammer with a nail (tool object relationship knowledge). 2. A patient may have lost knowledge as to what type of mechanical action is performed by a given tool or what type of mechanical action is needed to complete an act (tool action relationship knowledge). For example, when given a hammer, one should pound rather than twist. 3. Lastly, a patient may fail to understand the mechanical nature of problems as well as the mechanical advantages that tool may afford (mechanical knowledge). In this grant, we plan to study these potential conceptual disorders in patients with lateralized brain damage. Although it is possible that tool-object knowledge, tool action knowledge and mechanical knowledge may be diffusely or bilaterally represented, it has been well established that in man much of our knowledge about the world is represented unilaterally or asymmetrically. We therefore want to learn if the concepts about tool use are also asymmetrically or unilaterally presented. De Renzi, et al. suggested that ideational apraxia is associated with language comprehension disorders. Our planned studies will attempt to learn if these conceptual disorders are or are not related to language comprehension disorders. We also want to learn if disorders of the praxis conceptual system are related or can occur independently of disorders in the praxis production systems. Lastly, we want to learn the nature of the anatomic lesions that are associated with these praxis executive disorders.